1. Field of the Invention
This patent specification relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming and effectively performing a sheet transfer.
2. Description of Related Art
Conventionally, sheet feeders for separating stacked sheet materials one by one to feed them from the topmost one are classified into a corner tab separation type which presses both ends in the width direction on the leading edge of a sheet material in a feeding direction with tab members for separation; a separation pad type which urges a friction member to separate a sheet material; a bank separation type which runs sheet materials into a fixed gate member having a slope for separating the sheet materials one by one; and so on.
Among these types of sheet feeders, the known separation pad type sheet feeder, or the bank separation type sheet feeder discussed, for example, in Laid-open Japanese Patent Application No. 8-91612 are preferred since they require a low number of parts, but can be applied to a variety of different sheet materials (for example, post cards, envelopes, OHP (over head projector) sheets and so on) of different sizes including thick and thin materials in the same configuration at a low cost.
However, a conventional sheet feeder of the separation pad type generates noise due to friction slip, when a sheet material is being conveyed, sandwiched between a sheet feed roller and a friction member, particularly in a low cost, low speed machine operating 10 PPM (an image forming speed of 10 sheets per minute) or less. To prevent such noise, it is necessary to form the sheet feed roller in a semilunar shape. This leads to a requirement of a pair of cylindrical collars each having a diameter slightly smaller than that of the sheet feed roller additionally disposed coaxially with the sheet feed roller on both sides thereof for preventing a sheet stack stacking member from lifting up. Consequently, the number of parts is increased to result in a higher cost.
Recently, as recycled paper is increasingly used, sheet materials such as post cards and envelopes often having burred leading edges in a conveying direction, possibly produced in a cutting operation, cause an extra conveying load, so that the separation pad type sheet feeder can fail to feed sheet materials.
Further, back sides of once used sheet materials are also increasingly used, in which case stacked sheet materials differ in friction coefficient from one another so that two or more sheet materials may be fed at one time. A once used sheet material may be curled during fixation depending on a particular environment. Thus, a sheet material separator may be burdened with a greater load due to a curled leading edge of a sheet material depending on a direction in which the sheet material is curled, and may fail to separate the sheet materials for conveying them one by one.
It should be noted that the separation pad type sheet feeder presses a plane portion of a pad onto a sheet feed roller, so that the angle of a separation pad to a direction in which a sheet material fed from a stack is conveyed (corresponding to a displacement angle of a sheet material stacking member such as a bottom board) must be limited within a predetermined range. To conform to this limitation, the sheet feed roller is also limited in diameter, and the degree of freedom in layout is also restricted, thereby giving rise to a problem that the sheet feeder cannot be reduced in size.
On the other hand, the bank separation type sheet feeder discussed in Laid-open Japanese Patent Application No. 8-91612 includes a tilt member in contact with a sheet feed roller, which has a flat upper edge and a wide nip region with the sheet feed roller, so that variations in the member or the like can make it difficult to arrange the tilt face at a predetermined tilt angle.
When the topmost sheet material is being conveyed in an image forming unit, the sheet feed roller generally is not driven by the mechanism that rotates it to feed a sheet from the stack. However, while a previous sheet material is nipped between the sheet feed roller and a gate member, the sheet feed roller is rotated due to the friction force with the sheet material, and as the trailing edge of the previous sheet material passes the nip region, the leading edge of the next sheet material is sent to the tilt member by the associated rotation of the sheet feed roller.
In this event, if a friction coefficient between sheet materials is high or varies greatly, and the friction coefficient between the previous sheet material and the next sheet material is lower than the friction coefficient between the next sheet material and the sheet material subsequent to the next sheet material, the next sheet material can go beyond the tilt member to result in multiple sheet feeding.
Generally, in a sheet feeder which removably supports, through an opening of the feeder body, a cassette having a sheet material stacking member which has one end supported for pivotal movement and a free end urged upward, a tilt member and a sheet material separator in pressing contact with a sheet feed roller are positioned deep in the feeder body. Therefore, if a user attempts to draw out the cassette which contains few sheet materials, the sheet material stacking member may be caught in the feeder body, to keep the user from drawing out the cassette.
To overcome such a problem, as illustrated in FIG. 54, a conventionally known sheet feeder has a pair of protruding arms 1c (only one of which is shown in FIG. 54) integrally arranged on both sides of a bottom board 1, which is a sheet material stacking member having one end supported by a shaft 1a for pivotal movement within a cassette 11 and a free end urged upward at all times by a compression spring 3, and guide rails 10c formed on a feeder body 10 corresponding to the arms 1c, such that as the cassette 11 is drawn in a direction indicated by an arrow Y, the arms 1c come in contact with the guide rails 10c and lower the bottom board 1 against an urging force of the compression spring 3 as illustrated in FIG. 55, and the bottom board 1 is held at the lowered position by a known stopper means when the cassette 11 is drawn out.
However, although such a sheet feeder can prevent the bottom board 1 from being caught when the cassette 11 is drawn out, the tilt member is pressed onto the sheet feed roller 4 by the compression spring 5 after a sheet material has been fed before the cassette 11 is drawn out, so that the leading edge of the next sheet material 2n may remain nipped by the sheet feed roller 4 after the previous sheet has been fed (see FIG. 55).
If the cassette 11 is drawn out to supply sheet materials and again set in the sheet feeder, a remaining sheet material 2n within the feeder body 10 is crushed by the set cassette 11 to block the separator comprised of the tilt member 6, resulting in an inability of the sheet feeder to feed sheet materials.
To solve this problem, a conventional sheet feeder includes means associated with a movement of a drawn cassette to release the pressure of the tilt member. Another conventional sheet feeder provides a cassette with a separate arm for raking out the leading edge of a nipped sheet material. A further conventional sheet feeder senses a movement of a drawn cassette to rotate the sheet feed roller in a direction reverse to a sheet feeding direction to remove the leading edge of a sheet material from a nip region.
Among these conventional techniques, the first and third sheet feeders require an increased number of parts and increased steps for assembly to introduce a lower production efficiency. The second sheet feeder, on the other hand, can cause sheet material to tear and remain near the nip region, depending on the material, since the arm attempts to rake out the sheet material, as it is, nipped by a pressure applied by the tilt member and a pressure applied by the leading edge of the bottom board.
Furthermore, a sheet feeder which has an inclined bottom board for stacking sheet materials, positioned on the back surface or the like of an image forming apparatus, may cause skewing of sheet material that has one side fixed by a sheet material convey guide for structural reasons. A solution for this problem has been desired.
An image forming apparatus, simple in configuration, generally relies on a common motor for driving a sheet feeder and for driving an image forming section, so that a reduction in a load on the driving motor has been desired.
In addition, if a large number of sheet materials, the leading edges of which are uneven, are set in this type of sheet feeder, a conveyed sheet could be caught by the sheet feed roller and its leading edge damaged thereby. If the user is not aware of such a caught sheet and leaves it there, a paper jam is likely to occur when a sheet material is fed.
This patent specification describes a novel sheet feeder that separates sheet materials stacked on a pivotable sheet material stacking member one by one from the topmost sheet material so as to feed each of the sheet materials. In one example, a novel sheet feeder includes a sheet feed roller and a tilt member. The sheet feed roller is configured to come in pressing contact with the topmost sheet material for feeding the sheet material to a separator. The tilt member is configured to come in pressing contact with the sheet feed roller and includes a tilt face. In this configuration, the sheet feed roller has a front end running against the tilt face and a contact face in contact with the sheet feed roller, in the shape of an edge along an axial direction of the sheet feed roller.
In the foregoing sheet feeder, the tilt member may be in pressing contact with the sheet feed roller for pivotal movement with respect to the sheet feed roller, and may include translating means for advancing and retracting the tilt member in parallel to the sheet feed roller. The translating means is preferably comprised of a rib formed on one of the tilt member or a feeder body, and a guide rail formed on the other.
In the sheet feeder described above, the tilt member preferably has a contact face, the length of which is smaller than an axial length of the sheet feed roller, and more preferably is formed of a synthetic resin and includes a metal plate for covering at least the contact face with the sheet feed roller. The metal plate is preferably elastic. The elastic metal plate may be mounted from the tilt face so as to surround the tilt member on both upper and lower sides.
The distance in a sheet material convey direction between a location of the sheet feed roller at which the tilt member is in pressing contact with the sheet feed roller and a location of the sheet feed roller at which a sheet stacked on the sheet material stacking member comes in contact with the sheet feed roller preferably is in a range of 2 mm to 6 mm, and the angle of the tilt face of the tilt member to the sheet material convey direction preferably is set in a range of 50xc2x0 to 70xc2x0.
The sheet feeder may further include a thin elastic member disposed at a location downstream of a contact area of the sheet feed roller with the tilt member such that the thin elastic member crosses a tangential direction of the contact area. The thin elastic member may include two members disposed on both sides of the sheet feed roller, or may be disposed substantially at the center of the sheet feed roller.
The sheet feeder may further include a thin elastic member crossing the tangential direction of the contact area at a location downstream of the contact area of the sheet feed roller with the tilt member, wherein the thin elastic member includes a bent in the shape of hook bent toward the sheet feed roller at a rear end. The thin elastic member may include two members disposed on both sides of the sheet feed roller, or may be disposed substantially at the center of the sheet feed roller. The thin elastic member is disposed to cross the tangential direction at an angle ranging from 20xc2x0 to 60xc2x0.
The sheet feeder may further include a friction member which crosses a tangential direction of a contact area of the sheet feed roller in contact with the tilt member at a location downstream of the contact area. The friction member may include two members disposed on both sides of the sheet feed roller, or may be disposed substantially at the center of the sheet feed roller.
The sheet feeder may further include a pressure lever having a free end configured to come in contact with and move away from the sheet material stacking member, a sensing lever mounted coaxially with the pressure lever for pivotal movement associated with insertion/removal of a cassette having the sheet stacking member, and an elastic member disposed between the sensing lever and the pressure lever.
The pressure lever may be pivotally moved in association with the sensing lever when an angle of the pressure lever to the sensing lever is greater than a predetermined angle. In addition, the sensing lever may include a pair of arms at a free end thereof, wherein the arms extend from both sides of the tilt member, and the sensing lever pivotally moves to cause the arms to pass both sides of the contact area of the tilt member.
The sensing lever preferably includes spring pressure changing means for adjusting an urging force of a compression spring for pressing the tilt member onto the sheet feed roller.
The sheet feeder may further include a spring bearer disposed slidably in an axial direction of the compression spring on the opposite side of the compression spring with respect to the tilt member, wherein the spring pressure changing means engages with and disengages from the spring bearer associated with pivotal movement of the sensing lever, and the spring pressure changing means drives the spring bearer toward the tilt member when the spring pressure changing means engages with the spring bearer.
The sheet feeder may further include first cams disposed coaxially with the sheet feed roller for separating the sheet material stacking member from the sheet feed roller when the first cams come in contact with both side ends of a front face of the sheet material stacking member. The sheet material stacking member may include pressor ribs on both side ends at the front face thereof, such that the first cams come in contact with the pressor ribs.
The sheet feeder may further include second cams disposed coaxial with the sheet feed roller for separating the tilt member from the sheet feed roller when the second cams come in contact with both side ends of the tilt member. The tilt member may include ribs at both side ends, such that the second cams come in contact with the ribs.
The sheet feeder may further include a tilt member holder plate between the second cams and the tilt member. The tilt member holder plate has an opening formed for avoiding a site at which the sheet feed roller comes in contact with the tilt member, and a leading end spaced apart from the sheet material stacking member.
The present patent specification further discloses a novel image forming apparatus. In one example, a novel image forming apparatus includes a sheet feeder and an image forming mechanism. The sheet feeder separates sheet materials stacked on a pivotable sheet material stacking member one by one from the topmost sheet material so as to feed each of the sheet materials. The sheet feeder includes a sheet feed roller and a tilt member. The sheet feed roller is configured to come in pressing contact with the topmost sheet material for feeding the sheet material to a separator. The tilt member is configured to come in press contact with the sheet feed roller and includes a tilt face. The sheet feed roller has a front end running against the tilt face. The tilt member has a contact face in contact with the sheet feed roller in the shape of an edge along an axial direction of the sheet feed roller. The image forming mechanism is configured to form an image on a sheet material fed out from the sheet feeder.
The present patent specification further discloses a novel method of sheet feeding. In one example, a novel method of sheet feeding includes the steps of causing and making. The causing step causes a sheet feed roller to come in pressing contact with the topmost sheet material stacked on a pivotable sheet material stacking member so as to feed the sheet material to a separator. The making step makes a tilt member come in pressing contact with the sheet feed roller. The tilt member includes a tilt face. The sheet feed roller has a front end running against the tilt face. The tilt member has a contact face in contact with the sheet feed roller in the shape of an edge along an axial direction of the sheet feed roller.
The present patent specification further discloses a novel method of image forming. In one example, a novel method of image forming includes the steps of causing, making, and forming. The causing step causes a sheet feed roller to come in pressing contact with the topmost sheet material stacked on a pivotable sheet material stacking member so as to feed the sheet material to a separator. The making step makes a tilt member come in pressing contact with the sheet feed roller. The tilt member includes a tilt face. The sheet feed roller has a front end running against the tilt face. The tilt member has a contact face in contact with the sheet feed roller in the shape of an edge along an axial direction of the sheet feed roller. The forming step forms an image on the sheet material fed out from the sheet feeder.